Commerce Secretary Wilbur Ross faced a grilling from House Oversight Committee Democrats on Thursday about whether he lied to Congress about his controversial decision to add a citizenship question to the 2020 census.

"We have very serious questions about whether Secretary Ross was truthful when he appeared before Congress last year and testified on three occasions that he added the citizenship question only because of the department of justice requested it," the committee's chairman, Elijah Cummings, said in his opening remarks.

"The key question we will ask Secretary Ross today is, what was he hiding from the Congress?" the Maryland Democrat continued. "What's the real reason that Trump wanted to add this unconstitutional question?"

Ross tried to clarify his rationale for adding that question in his opening remarks, saying that before he decided to add the question, he learned that the Justice Department might have wanted it included.

"I instructed staff to follow up with DOJ for a written statement confirming whether or not DOJ was going to ask for reinstatement of the question," Ross said. "I wanted to make sure that we had enough time to adequately consider any formal request that DOJ might make."

"Ultimately, on December 12, 2017, DOJ made a formal written request that the Census Bureau reinstate the citizenship question on the decennial census," Ross said. "DOJ sought census block-level citizenship data for use in Voting Rights Act enforcement. In response, the Census Bureau initiated a legal, policy, and programmatic review process to consider alternate means of meeting DOJ's request."

Ross testified before the House Ways and Means Committee last March that the question was added at his direction after he received the DOJ request. But documents released as a part of a multi-state lawsuit against Ross showed that the secretary inquired about adding the question much earlier.

Ross' highly-anticipated appearance before the committee on Thursday comes only days after a second federal judge said he violated federal law and the Constitution by hastily adding the question to the upcoming survey.

Republicans on the Oversight Committee excoriated Democrats in their opening remarks, accusing the party of politicizing the process and defended the decision to add the question to the census. They also attempted to adjourn the hearing, arguing that it could influence a decision by the Supreme Court decision on the issue, which it plans to take up next month.

"I mean, for the life of me, I do not know why the Democrats don't want to know how many citizens are in the United States of America," ranking member Rep. Jim Jordan, R-Ohio, said. "But for some reason, they are focused on this question. Maybe it's politics. It seems clear to me we are having the hearing today for that reason. The majority insists on politicizing the 2020 census."

Mark Meadows, R-N.C., later added, "Many of the questions that you will receive today have nothing to do with accurately counting the number of people that are here in the United States of America. It has everything to do with politics. And everything to do with trying to make sure that one particular message comes across."